A unique species of fanged frog discovered in Indonesia has found a way around the whole egg-laying thing, researchers report; it gives birth to live tadpoles, the first species known to do so.

Most frogs are egg layers, and while there are a few species that give birth to live froglets, the newborn tadpoles of the fanged frogs of Sulawesi Island in Indonesia were unknown to science, the researchers say.

Most of the world's 6,000 species of frogs lay eggs, which the males then fertilize externally with released sperm.

"But there are lots of weird modifications to this standard mode of mating," says Jim McGuire from the University of California, Berkeley, part of an international research team reporting the new species dubbed Limnonectes larvaepartus.

Frogs in the family Limnonectes are called fanged frogs for the twin projections on the lower jaw, used in fighting.

On Sulawesi, east of Borneo, McGuire stumbled on what he thought was a single male frog. But when he picked it up he suddenly found he was holding a pregnant female frog and, a moment later, a handful of wriggling tadpoles.

"This new frog is one of only 10 or 12 species that has evolved internal fertilization, and of those, it is the only one that gives birth to tadpoles, as opposed to froglets or laying fertilized eggs," McGuire says.

How the males of the newly discovered species manage to fertilize the eggs while they are still within the female is still unknown, the researchers say, because they don't posses any conventional sexual organs with which to deliver the sperm.

The new finding of Limnonectes larvaepartus comes "totally out of the blue," says Ben Tapley of the Zoological Society of London.

Four species of fanged frog have been discovered on Sulawesi, although researchers say they suspect there may be many more.

"They're relatively dull frogs, actually," Tapley says. "To find out something totally surprising about a frog you would barely notice in the forest is really cool."

"Finding a new species is not that rare -- but actually discovering a new reproductive mode is."

The area where L. larvaepartus was identified has one of the highest rates of deforestation in the world and that, along with climate change, disease and development, threatens many frog species with extinction.

"It's great that we're learning about these species before it's too late," Tapley says.

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